Probe having at least one magnetic resistive element for measuring leakage magnetic field

ABSTRACT

A probe for measuring a leakage magnetic field includes a substrate, a flexible cantilever having one end fixed to the substrate and a free end, and at least one magneto resistive element arranged on the free end of the cantilever. The magneto resistive element has a width within a range from 10 nm to 1 μm as measured in a direction perpendicular to a longitudinal direction of the cantilever and in a direction in which the cantilever can be deflected.

TECHNICAL FIELD

The present invention relates to a probe for measuring a leakagemagnetic field, comprising at least one magneto resistive element. Theprobe according to the present invention is applied to a microscope, anIC or the like.

BACKGROUND OF INVENTION

A microscope measuring a magnetic structure of a surface of a magneticsubstance is known as a magnetic force microscope (MFM), a scanningnear-field optical microscope (SNOM) or a scanning magneto-resistivemicroscope (SMRM), for example.

As the MFM measures a gradient of a leakage magnetic field from asample, it is difficult to obtain a distribution of a leakage magneticfield and a magnetic structure of the sample from a value measured bythe MFM. The SNOM makes use of a magneto-optical effect near a magneticfield; however, it is difficult to analyze data measured by the SNOMquantitatively because a physical phenomenon about the magneto-opticaleffect near the magnetic field is not clear and there is difficulty incontrolling polarization at the proximity field.

The SMRM measures the leakage magnetic field from the sample directlywith a magneto resistive (MR) element; therefore, the quantitativemeasurement in the SMRM is easier than that in the MFM and the SNOM. Asto the SMRM, a basic experiment is reported in IEEE. Trans. Mag. 33(1)891 (1997). Such a SMRM is also disclosed in JP-A-6-59004 andJP-A-10-19907.

However, a conventional probe as described in JP-A-6-59004 andJP-A-10-19907 has the MR element with a relatively large width at theorder of several um, so that it is difficult to obtain a magneticinformation at a relatively high resolution with the conventional probe.In order to improve the resolution of the conventional probe, it isnecessary to design the conventional probe specially by junction of amagnetic probe onto a surface of the MR element or the like. As aresult, a method of manufacturing the probe is complex and it isdifficult to mass-produce the probes with a relatively high resolutionat a relatively high yield.

DISCLOSURE OF INVENTION

It is an object of the present invention to provide a probe with arelatively high resolution capable of being mass-produced at arelatively high yield.

According to the present invention, there is provided a probe formeasuring a leakage magnetic field, comprising: a substrate; a flexiblecantilever having one end fixed to the substrate and a free end; and atleast one magneto resistive element arranged on the free end of thecantilever. The magneto resistive element has a width within a rangefrom 10 nm to 1 μm as measured in a direction perpendicular to alongitudinal direction of the cantilever and in a direction in which thecantilever can be deflected.

The probe according to the present invention makes use of a propertythat the resolution of the MR element improves as the width of the MRelement becomes small in a direction perpendicular to the longitudinaldirection of the cantilever and in a direction in which the cantilevercan be deflected (magneto-sensitive direction). According to the presentinvention, by having the width of the MR element not more than 1 μm atthe magneto-sensitive direction, it is possible to detect the leakagemagnetic field with a wavelength of not more than 10 μm without junctionof the magnetic probe onto the surface of the MR element. As a result,it is possible to mass-produce the probes with a relatively highresolution at a relatively high yield. It is possible to form the MRelement having the width not more than 1 μm at the magneto-sensitivedirection with a lithographic technique such as an electron beamlithography.

The smaller the width of the MR element at the magneto-sensitivedirection, the shorter the wavelength in the leakage magnetic field thatcan be detected. If, however, the width of the MR element is smallerthan 10 nm at the magneto-sensitive direction, the MR element may nothave the above-mentioned property because a magnetization in a magneticsubstance film composing the MR element fluctuates as a result of athermal oscillation of the magnetization. As a result, it is necessaryto have the width of the MR element be not less than 10 nm at themagneto-sensitive direction.

The MR element may be, for example, an anisotropic magneto resistive(AMR) element comprising at least one magnetic substance film, a giantmagneto resistive (GMR) element comprising a multilayer structurecomposed of at least one magnetic substance film and at least onenon-magnetic substance film or a tunneling magneto resistive (TMR)element comprising a tunnel junction of magneticsubstance-insulator-magnetic substance.

Preferably, the probe according to the present invention furthercomprises a resistor-bridge circuit electrically connected to themagneto resistive element. Thereby, it is possible to reduce noiseresulting from wiring external to the cantilever. As a result, it ispossible to further improve the accuracy of a measurement by the probethat is capable of being mass-produced at a relatively high yield.

Preferably, the probe according to the present invention furthercomprises a stylus connected to the MR element. Thereby, it is possibleto maintain a good tracking property for the position control on theface of the sample even if the sample having relatively large unevennessis measured. As a result, it is possible to further improve the accuracyof the measurement by the probe capable of being mass-produced at arelatively high yield. It is not necessary to apply a complex process ofthe conventional method of manufacturing the probe when the stylus isconnected to the MR element. The stylus may be a carbon nanotube or awhisker composed of a magnetic substance.

According to the present invention, there is provided a probe measuringa leakage magnetic field, comprising: a substrate; a flexible cantileverhaving one end fixed to the substrate and a free end; at least twomagneto resistive elements each arranged on the free end of thecantilever; and means for determining the leakage magnetic field inrelation to a dependency along with a direction with which the magnetoresistive elements are provided. The magneto resistive elements eachhave a width within a range from 10 nm to 1 μm as measured in adirection perpendicular to a longitudinal direction of the cantileverand in a direction in which the cantilever can be deflected.

Thereby, it is possible to measure the leakage magnetic field inrelation to a dependency along with a direction with which the MRelements are provided continuously, for example, a direction parallel toa height of the probe, and it is also possible to measure a distributionof a height in the magnetic field at a relatively high resolution.

There is provided a method of manufacturing a probe comprising steps of:providing a layer composed of a flexible material on one face of asubstrate; forming by a lithographic technique at least one MR elementon the layer; and removing a part of the substrate to form a cantileverhaving one end fixed to the substrate and the free end arranged with theat least one MR element.

According to the method, as the at least one MR element is formed withthe lithography, it is possible to form the MR element having a widthnot more than 1 μm at the magneto-sensitive direction. As a result, itis possible to mass-produce the probes with a relatively high resolutionat a relatively high yield. The lithography is an electron beamlithography and so on.

Preferably, the magneto resistive element has a width within a rangefrom 10 nm to 1 μm as measured in a direction perpendicular to alongitudinal direction of the cantilever and in a direction in which thecantilever can be deflected.

Preferably, the method further comprises a step of forming aresistor-bridge circuit on the cantilever, the resistor-bridge circuitbeing electrically connected to the MR element. Thereby, it is possibleto mass-produce the probes with an improved accuracy of the measurementat a relatively high yield.

Preferably, the method further comprises a step of connecting a stylusto the MR element. Thereby, it is possible to mass-produce the probeswith the improved accuracy of the measurement at a relatively highyield. In this case, the stylus may be a carbon nanotube or a whiskercomposed of a magnetic substance.

Preferably, the number of MR elements is no fewer than two. Thereby, itis possible to measure the leakage magnetic field in relation to adependency along with a direction with which the MR elements areprovided continuously, for example, a direction parallel to a height ofthe probe. It is also possible to measure a distribution of a height inthe magnetic field at a relatively high resolution.

The present invention also provides a microscope comprising a probemeasuring a leakage magnetic field, the probe comprising: a substrate; aflexible cantilever having one end fixed to the substrate and a freeend; and at least one magneto resistive element arranged on the free endof the cantilever; wherein the magneto resistive element has a widthwithin a range from 10 nm to 1 μm as measured in a directionperpendicular to a longitudinal direction of the cantilever and in adirection in which the cantilever can be deflected.

Because the microscope comprises the probe capable of beingmass-produced at a relatively high yield and having a superiorperformance, the microscope also has a superior performance.

Preferably, a direction of a thickness of the MR element issubstantially parallel to a direction of the leakage magnetic field.Thereby, it is possible to realize the microscope with a higherresolution.

The present invention also provides a tester comprising a probemeasuring a leakage magnetic field, the probe comprising: a substrate; aflexible cantilever having one end fixed to the substrate and a freeend; and at least one magneto resistive element arranged on the free endof the cantilever; wherein the magneto resistive element has a widthwithin a range from 10 nm to 1 μm as measured in a directionperpendicular to a longitudinal direction of the cantilever and in adirection in which the cantilever can be deflected.

As the tester comprises the probe capable of being mass-produced at arelatively high yield and having a superior performance, the tester hasa superior performance.

Embodiments of the probe according to the present invention will bedescribed with reference to drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1(a) to 1(h) are schematic diagrams explaining a method ofmanufacturing a probe according to the present invention;

FIG. 2 is a perspective view of a probe according to the presentinvention;

FIG. 3 is a side view of a probe according to the present invention;

FIG. 4 is a graph showing a relation between a recording wavelength andan output of the magneto resistive element;

FIG. 5 is a top view of another probe according to the presentinvention;

FIG. 6 is a side view of another probe according to the presentinvention;

FIG. 7 is a perspective view of another probe according to the presentinvention;

FIG. 8 is a side view of another probe according to the presentinvention;

FIG. 9 is a side view of another probe according to the presentinvention;

FIG. 10 is a side view of another probe according to the presentinvention;

FIG. 11 is a top view of another probe according to the presentinvention;

FIG. 12 is a microscope comprising a probe according to the presentinvention; and

FIG. 13 is a tester comprising a probe according to the presentinvention.

BEST MODE FOR CARRYING OUT THE INVENTION

FIGS. 1(a) to 1(h) are schematic diagrams explaining a method ofmanufacturing a probe according to the present invention. Firstly, asilicon wafer as a substrate is prepared and nitride films 2, 3 areformed on both sides of the silicon wafer 1, respectively, using a lowpressure CVD. Then, the nitride films 2, 3 are etched withphotolithography and a reactive ion etching to remove a part of thenitride film 2 in order to form a cantilever, and to remove a part ofthe nitride film 3 in order to be etched a part of the silicon wafer 1in an after process, so that alignment marks 4, 5 for an electron beamlithography used in a next process are formed. A side and a top of apart obtained as such are shown in FIGS. 1(a) and 1(b).

Next, an MR element 6 is formed with the electron beam lithography and avapor deposition at a portion to be a tip of the cantilever. In thiscase, a size of the MR element 6 can be not more than 0.1 μm×0.1 μm. Aside and a top of a part obtained as such are shown in FIGS. 1(c) and1(d).

Next, lead electrodes 7, 8 are formed with the electron beam lithographyand the vapor deposition, and a silicon nitride film or a silicon oxidefor protection is formed on a surface of the MR element 6 and the leadelectrodes 7, 8. Then, bonding pads 9, 10 are formed. A side and a topof a part obtained as such are shown in FIGS. 1(e) and 1(f).

Next, a part of the substrate 1 is etched from a back face of thesubstrate 1 with an anisotropic etching. In this case, a throwing powerof an etchant at a face in which the MR element 6 is arranged isprevented so that a part of the substrate 1 is left. Then, a part of thesubstrate 1 is removed with the reactive ion etching or a sputtering.Finally, a tip of a cantilever 11 is trimmed with a focusing ion beam. Aside and a top of a part obtained as such are shown in FIGS. 1(g) and1(h).

In the embodiment, the MR element 6 has a width within a range from 10rim to 1 μm as measured in a direction perpendicular to a longitudinaldirection of the cantilever 11 and in a direction in which thecantilever can be deflected (magneto-sensitive direction). The MRelement 6 is an AMR element comprising at least one magnetic substance,a GMR element comprising at least one magnetic substance and at leastone non-magnetic substance or a TMR element comprising a tunnel junctionof magnetic substance-insulator-magnetic substance, for example.

A perspective view and a side view of the probe obtained in accordancewith the embodiment are shown in FIGS. 2 and 3. As the width of the MRelement 6 is within a range from 10 nm to 1 μm at the direction of themagneto-sensitive direction, the tip of the cantilever 11 functions as aprobe for a position control.

FIG. 4 is a graph showing a relation between a recording wavelength andan output of the magneto resistive element. In this case, an MR elementoutput when measuring a magnetic field of a magnetic recording medium iscalculated. In FIG. 4, curves a to e represent characteristics when thewidth w of the MR element is 5 μm, 1 μm, 0.5 μm, 0.1 μm and 0.05 μm atthe magneto-sensitive direction, respectively. In this case, a currentdensity of the MR element is 10¹¹A/m².

It is apparent from FIG. 4 that a recording wavelength becomes short asthe width of the MR element becomes short at the magneto-sensitivedirection. When the width of the MR element is not more than 1 μm at themagneto-sensitive direction, it is possible to detect the recordingwavelength not more than 10 μm, in other words, leakage magnetic fieldwith a wavelength not more than 10 μm. As a result, it is possible tomass-produce probes with a relatively high resolution and a superioryield factor without junction of the magnetic probe onto the MR elementin the prior art.

In the lithographic technique, the lower limit of the length of the MRelement is several nm at the magneto-sensitive direction. However, asthe width of the MR element at the magneto-sensitive direction becomessmall, an effect of a thermal oscillation for a magnetization of the MRelement composed of magnetic substance film is remarkable. The lowerlimit of the width of the MR element at the magneto-sensitive directionis given by the following condition in which a magnetic anisotropicenergy fixing the magnetization equals to an energy of the thermaloscillation:

vK=kT/2.

In this case, v represents a volume of the MR element, K represents themagnetic anisotropic energy per unit volume of a magnetic substancecomposing the MR element, k represents Boltzmann constant, and Trepresents an absolute temperature.

The magnetic anisotropic energy per unit volume of the magneticsubstance composing the MR element is around 5×10³ J/m³, and the lengthv⁻³ (=w) of the MR element at the magneto-sensitive direction is 10 nmat a room temperature (T=300K).

FIG. 5 is a top view of another probe according to the presentinvention. In the embodiment, by properly selecting a wiring pattern oflead lines 12 a, 12 b for electrical connection to an MR element 12 cand material composing the lead lines 12 a, 12 b, and forming aresistor-bridge circuit 14 for electrical connection to MR element 12 cthrough the lead lines 12 a, 12 b on a cantilever 13, noise resultingfrom an external wiring of the cantilever 13 is reduced. Thereby, theaccuracy of a measurement by probe further improves. In this case, alaser or a focusing ion beam is used when trimming the resistor-bridgecircuit 14.

FIG. 6 is a side view of another probe according to the presentinvention. In the embodiment, a stylus 22 is connected to a MR element21. Thereby, a sensitivity of a magnetic field in the probe furtherimproves, and it is possible to maintain a good tracking property forthe position control on a face of a sample even if a sample havingrelatively large unevenness is measured. The stylus 22 is composed of acarbon nanotube or a whisker composed of a magnetic substance, forexample.

FIG. 7 is a perspective view of another probe according to the presentinvention. As shown in FIG. 7, a multi-probe or a probe array can becomposed by a plurality of the probes according to the presentinvention.

FIG. 8 is a side view of another probe according to the presentinvention. In the embodiment, a plurality of MR elements 31, 32 and 33are formed on one cantilever 34. Thereby, the MR elements 31 to 33 canmeasure a magnetic resistance along with a direction A on which the MRelements 31 to 33 are arranged continuously.

FIG. 9 is a side view of another probe according to the presentinvention. In the embodiment, an MR element 41 is arranged so that adirection of the thickness of the MR element 41 substantially coincideswith a direction B of a magnetic field. Thereby, it is possible torealize the probe with a relatively high resolution.

FIG. 10 is a side view of another probe according to the presentinvention. In the embodiment, a plurality of MR elements 51, 52 and 53are formed on one cantilever 54 and a stylus 55 is connected to the MRelement 51. Thereby, it is possible to measure a magnetic distributionalong a direction C of a height of the probe at a relatively highaccuracy.

FIG. 11 is a top view of another probe according to the presentinvention. In the embodiment, a plurality of MR elements 61, 62, 63, 64,65 and 66 are formed on one cantilever 67. Thereby, it is possible tomeasure a magnetic distribution along a direction D of a height and adirection E of a width of the probe.

FIG. 12 is a microscope comprising a probe according to the presentinvention. The microscope comprises a probe 71 according to the presentinvention, a PZT tube 73 on which a sample 72 is deposited, a currentgenerator 74 connected to the sample 72, a laser diode 75 radiating alaser beam to the probe 71, a magnet 76 generating a magnetic field, aphotodiode 77 receiving the laser beam reflected from the cantilever 71,an AFM controller 78 supplied with a signal from the photodiode 77, acurrent generator 79 and a pre-amplifier 80 connected to the probe 71, asecondary amplifier 81 connected to the pre-amplifier 80, and areference voltage 82 and a low-pass filter 83 connected to the secondaryamplifier 81.

The AFM controller 78 controls an operation of the PZT tube 73 in threedimensional coordinate system. In the embodiment, it is possible tomeasure the leakage magnetic field from a surface of the sample 72quantitatively, and apply to an observation of a magnetic structure on asurface of the magnetic body and measurement of a distribution of theleakage magnetic field of a magnetic recording head.

FIG. 13 is a tester comprising a probe according to the presentinvention. In the embodiment, a current through the wiring is measuredby measuring the distribution of the leakage magnetic field from aconsiderably small width of the wiring on a substrate 91. It is alsopossible to analyze the distribution of the magnetic field resultingfrom the wiring of a multilayer and measure the current in themultilayer portion by measuring the distribution of the leakage magneticfield.

While the present invention has been described above with reference tocertain preferred embodiments, it should be noted that they werepresented by way of examples only and various changes and/ormodifications may be made without departing from the scope of theinvention. For example, the electron beam lithography is used whenforming the MR element in the above-mentioned embodiment; however, anyother type of lithographic technique can be used. The probe according tothe prevent invention is applied to the microscope and the tester;however, it can be used in any other application.

What is claimed is:
 1. A probe for measuring a leakage magnetic field,comprising: a substrate; a flexible cantilever having one end fixed tosaid substrate and a free end, said cantilever having a longitudinaldirection; and a magneto resistive element arranged on the free end ofsaid cantilever, said magneto resistive element having a width within arange from 10 nm to 1 μm as measured in a direction perpendicular tosaid longitudinal direction of said cantilever and in a direction inwhich said cantilever can be deflected.
 2. The probe according to claim1, wherein said magneto resistive element has an anisotropic magnetoresistive element comprising at least one magnetic substance film. 3.The probe according to claim 1, wherein said magneto resistive elementhas a giant magneto resistive element comprising a multilayer structurethat includes at least one magnetic substance and at least onenon-magnetic substance.
 4. The probe according to claim 1, wherein saidmagneto resistive element comprises a tunneling magneto resistiveelement having a tunnel junction that includes a first magneticsubstance, an insulator, and a second magnetic substance.
 5. The probeaccording to claim 1, further comprising a resistor-bridge circuitelectrically connected to said magneto resistive element.
 6. The probeaccording to claim 1, further comprising a stylus connected to saidmagneto resistive element.
 7. The probe according to claim 6, whereinsaid stylus comprises at least one carbon nanotube.
 8. The probeaccording to claim 6, wherein said stylus comprises at least one whiskerthat includes a magnetic substance.
 9. A probe measuring a leakagemagnetic field, comprising: a substrate; a flexible cantilever havingone end fixed to said substrate and a free end, said cantilever having alongitudinal direction; at least two magneto resistive elements, eacharranged on said free end of said cantilever, and each having a widthwithin a range from 10 nm to 1 μm in a direction perpendicular to saidlongitudinal direction and in a direction in which said cantilever canbe deflected; and means for determining said leakage magnetic field inrelation to a dependency along with a direction with which said magnetoresistive elements are provided.
 10. The probe according to claim 9,wherein each of said magneto resistive elements has an anisotropicmagneto resistive element comprising at least one magnetic substancefilm.
 11. The probe according to claim 9, wherein each of said magnetoresistive element has a giant magneto resistive element comprising amultilayer structure that includes at least one magnetic substance andat least one non-magnetic substance.
 12. The probe according to claim 9,wherein each of said magneto resistive elements comprises a tunnelingmagneto resistive element having a tunnel junction that includes a firstmagnetic substance, an insulator, and a second magnetic substance. 13.The probe according to claim 9, further comprising a resistor-bridgecircuit electrically connected to each of said magneto resistiveelements.
 14. The probe according to claim 9, further comprising astylus connected to each of said magneto resistive elements.
 15. Theprobe according to claim 14, wherein said stylus comprises at least onecarbon nanotube.
 16. The probe according to claim 14, wherein saidstylus comprises at least one whisker that includes a magneticsubstance.